Key assembly for vehicle ignition locks

Abstract

A method of decreasing resonant frequency shifting of an electrical circuit mounted on a vehicle key includes providing a frame in an opening in the head portion of a vehicle key and locating the transponder in the frame. The frame comprises substantially rigid non-metallic material, and the frame includes a support structure for supporting the transponder while decreasing forces produced on the transponder by thermal expansion and contraction of the head portion of the key, thereby decreasing shift in the resonance of the electrical circuit of the transponder. The frame, the transponder and the head portion of the key are overmolded providing an outer covering that encloses and protects the transponder.

Description

RELATED APPLICATIONS[0001]This application is a divisional of U.S. patent application Ser. No. 09 / 014,311 filed on Jan. 27, 1998 now U.S. Pat. No. 6,427,504, which is a continuation-in-part of U.S. patent application Ser. No. 08 / 503,429, filed Jul. 17, 1995 and issued on Mar. 14, 2000 as U.S. Pat. No. 6,035,677, which is a continuation-in-part of U.S. patent application Ser. No. 08 / 112,094, filed Aug. 26, 1993 and issued on Jul. 18, 1995 as U.S. Pat. No. 5,433,096.BACKGROUND OF THE INVENTION[0002]The present invention relates to an automobile security system, and more particularly, to a key assembly for use in a vehicle ignition and lock unit.[0003]Various types of security systems used in conjunction with the ignition circuit of a vehicle are known in the art. Many of these systems include anti-theft and / or anti-tampering mechanisms which are incorporated to deter the unauthorized use of vehicles. An electronic vehicle ignition lock is a component of some of these systems which can...

AI Technical Summary

Benefits of technology

[0017]Further in accordance with the invention, the injection molding process is conducted so as to minimize impact forces applied to the transponder during the molding process. Preferably, the undermold material is injected, in liquid form, through a gate that directs the material against a corner of the transponder causing the material to be split into two portions. Consequently, the liquid material that forms the undermold encircles the transponder as the material is being injected producing substantially even hydrostatic pressures. Encircling the transponder with the liquid material (which will eventually harden to form the undermold of the key assembly), substantially prevents the application of impact forces directly to the planar surfaces of the transponder, with an attendant reduction in the potential for damage to the transponder which could cause the device to fail.

[0018]In accordance with a feature of the invention, during the injection molding process, strategically located voids are formed in the undermold. These voids, which can be extremely small, eliminate pressure differentials which can otherwise develop between the adjacent portions of the mold. Eliminating the potential for a pressure differential prevents the transponder from shifting or cracking within the key assembly during overmolding.

[0019]Another benefit of molding the key assembly in two stages, namely first undermolding and subsequently overmolding, is that while the plastic is cooling following the injection molding process, overall heat and compressive force imposed on the transponder are substantially reduced. While the harder plastic material undergoes a greater degree of compression during cooling, the impact on the transponder is minimized because less material is used in forming the undermold.

[0020]Moreover, the component tending to cause a shift in the resonance of transponders for key assemblies used in RFID systems is substantially eliminated using the overmolding process provided by the invention. The softer plastic material which is used to form the overmold portion of the key head tends to abate thermal problems because the overmold material is less inclined to exert pressure and distort the transponder to the degree that harder material would. However, softer material is more prone to mechanical deformation by shear or torsional forces.

[0021]A further benefit of the present invention is the use of an injection molding device which supports and contains the transponder within the key assembly along its weakest axis to prevent cracking, fracturing, and other adverse effects, any of which can contribute to failure. The mold plates forming the molds that are used in molding the undermold and the overmold of the key assembly further serve to reduce, even prevent thermal excursion during manufacture of the key assembly because the mold plates function as heat sinks. The mold plates absorb auxiliary heat and thermal energy so that the affects of the heat upon the transponder in both the undermold and overmold processes are substantially reduced. Preferably, the mold plates comprise a relatively massive material with good heat transfer characteristics.

[0022]The improved process for manufacturing RFID systems incorporating known transponders, such as those produced by Texas Instruments, Inc. and Motorola, minimizes the impact and compressive force applied along the weak axis (or axes in the case of the Motorola device) of the transponder and, thus, reduces the chance that the transponder will fail.

Problems solved by technology

The inventors have found a problem involving a shift in inductance of the coil and the capacitance of the capacitor of the resonant circuit of the transponder which affects the operation of RFID security systems which occurs when the transponders are used in conjunction with prior key assembly designs.

A shift in the inductance and capacitance of the transponder's resonant circuit changes the resonant frequency of the transponder which can result in failure of the transponder to receive the interrogation signal being transmitted, or in the weakening of the strength of the signal sent to the receiver so that the receiver cannot detect signals transmitted by the transponder.

The end result is that the vehicle engine cannot be started and / or run using the ignition or otherwise.

However, the nature of harder plastic material is such that it tends to cause higher forces to be applied to the transponder under temperature excursions.

However, the softer material is more prone to mechanical deformation by externally applied forces.

This softer material can also adversely impact the structural integrity of the key head.

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